Underground conduit for electric conductors



(No Model.)

0. H. SEWALL. UNDERGROUND GONDUIT FOR ELECTRIC OONDUGTORS. No. 603,745.V Patented May 10, 1898.

"I lllll III III WITNESSES: INVENTOR UNITED STATES PATENT OFFICE.

CHARLES 'HENRYSEWALL, OF CHICAGO, ILLINOIS.

UNDERGROUND CONDUIT FOR ELECTRIC CONDUCTORS.

SPECIFICATION forming part of Letters Patent No. 603,746, dated May 10,1898.

Application filed May 8, 1895. Serial No- 548,613. (No model.)

To all whom it may concern:

Be it known that I, CHARLES HENRY SEW- ALL, a citizen of the UnitedStates, residing in Chicago, in the county of Cook and State ofIllinois,have invented certain new and useful Improvements inUnderground Conduits for Electrical Conductors, of which the followingis a specification.

My invention relates tov that class of structures which are composed ofsections of pipes joined end to end and laid in multiple to form a groupof ducts into which can be drawn electrical conductors or cables; andthe objects of my improvements are to create a conduit structure whichis practically without joints and which has great strength anddurability, and also to provide ducts of a shape better adapted to meetrequirements than eithenthe round-or square ones now in use.

Referring to the drawings, Figure 1 is a cross-sectional view showing'myconduit as a whole and ready for use. Fig. 2 is a view in perspective ofa single section G of the upper part of the duct. tion of G withwire-cloth embedded therein; Fig. 4, a wire bridge F, used for joiningsections G; Fig. 5, sections G Grv joined by bridge F.

The same letters represent the same parts in the different views.

A, Fig. 1, represents the soil filling a trench in which conduit B isburied.

O is the area bounded by a broken line indicating the space and positionin a duct which will be occupied bya cable of electrical conductors.

Gis an arch-shaped inverted channel which is the upper portion of aductin the conduit, and g is wire-cloth embedded in arch G.

F is a wire-cloth bridge used to connect sections G G.

Referring to Fig. 3, the letter a" is so placed as to show the uppermostpoint or apex of inside of arch G. t is the lowermost point orduct-floor line. sis a point half-waybetween r and t. The horizontalline 00 sis the line of meeting of the straight sides of arch G with thesemicircular top or roof. The line m n is horizontal through the centerof cable 0 when the latter is lying upon duct-floor line 25.

It is a factthat the'bond of iron and concrete, whereby the iron acts asa tension and Fig. 3 shows a cross-sec-.

the concrete as a compression member,affords a structural strength muchgreater than if theconcrete is used alone. It is necessary, however,that the tension member shall be immovable. Wire in the form of cloth (arectangular mesh being preferable) will not slip through set concrete,andrepeated experiments have shown that the full compressive strength ofthe concrete and nearly the full tensile strength of the iron wires inthe warp are the properties of a composite made by embedding wire-clothin a concrete of hydraulic cement and sand.

The arch-shaped channels shown in the drawings in sections about sixfeet in length are laid in multiple on a smooth fiat floor madecontinuous between manholes,said floor being of such horizontaldimension as is required for thenumber of ducts in each layer. Thearches are then fixed in place by a cement concrete which fills thespaces between them and covers their tops; and this cover- .ing can beleveled and smoothed to form a floor upon which a second series ofarches may be laid. The process continues, layer upon layer,until therequired number of ducts is formed.

At this writing underground conductors of electricity are almostinvariably, either singly or in groups, inclosed in a lead sheath,making them air and moisture proof. For convenience in making andhandling the leadcovered cable is round in cross sections. Good practiceadmits but one cable in each duct.

It is desirable that underground conduits should be formed frommaterials that are proof against corrosion by chemical action, that havesufficient hardness to turn off accidental strokes of digging-tools, andthe necessary strength to resist pressures caused by heavy weights onstreet-surfaces, and as the laying of sewers, gas-pipes, and water-mainsand their surfaces is a frequent source of trouble Sby reason of workmenundermining conduits there should be combined with the above qualitiesboth compressive and tensile strength to resist shearing forces. It maybe said also that while strains upon conduits are mainly from downwardpressures those in other directions are not unusual and should becarefully considered.

It will be seen that the form of duct shown in the drawings (see Figs. 1and 2) and the material of which the herein-described structure is madeare both well adapted to conduitwork.

The floor of my duct is preferably smooth and flat. .It can be madeslightly concave. The upper part has vertical sides surmounted by asemicircular roof, the radius of the inside surface of said roof (7" s,Fig. 3) being the same as the height of the straight sides, (5 t, Fig.3.) The advantages of this shape are that it combines the roominess of aflat floor with the supporting strength of the perpendicular walls underan arched roof.

The support given by the arches is much greater thanfif the ducts wereround, square, or semicircular in form.

or square and is but one-half of what would be occupied by an opening inthe form of a semicircle. For instance, if a semicircular opening isneeded to be three inches in height in order that a round cable of, say,two and one-half inches diameter may conveniently be drawn into it thenits radius will be three inches and the width of opening at base will bethe diameter or six inches, while with my arches the width at base willbe butthree inches. It can also be said that if the height of thestraight sides is greater than the radius of the semicircular roof spaceis wasted, because if there be drawn into the duct a round cable havinga diameter a little less than the width of the duct there will be aproportionall y-greater space between the top side of the cable and theapex of the arch, which additional space will increase the size andconsequent cost of the structure and will serve no the exact conditionof straight sides of the same height, as is the length of radius of roofsurmounting them, is the most economical of space and in every way thebest adapted to the function of a conduit-duct, although I do notlimitmyself to this specific preferred structure. I

In a pipe having a circular cross-section a cylindrical cable, which inpractice is more or less crooked, will wedge itself and bind against thesides of the pipe and its covering be subjected to injury from abrasion.Hence a further advantage of my duct form is that a cable which is beingdrawn into it can have as much sidewise swing as it would have in asquare duct, for as the round cross-section of the cable mustnecessarily be somewhat smaller than the opening through which it isdrawn then the greatest chord of said round cross-section, the diameter,(see line m n, Fig. 3,) will come below the line of greatest height ofthe perpendicular sides of the duct, (see The space occupied is exactlythe same as if the ducts were round line a; s, Fig. 3,) and consequentlythe cable cannot come into contact with any point on the surface of thesemicircular roof. Again, the arched roof, while in no way impeding themovements of the cables, is much stronger than the fiat roof of a squareduct, and the perpendicular supporting-sides upon a flat floor make amuch stronger foundation than the semicircular one which contributes theupholding strength of a round pipe.

Another feature of my invention is that the device herein shown escapesthe greatest peril that hasheretofore menaced all conduits laid insectionsviz., the settling and breaking of the structure at the joints.As my ductfioors are continuous for an entire division the weakness atjoints is overcomethat is to say, the lower part or floor of the duct isjointless and underlies the upper or sectional part. A Wire bridge F,Figs. 3 and 4, is used to bind together the upper sections.

Referring to Fig. 5, a strain upon any part of the conduit will beresisted by the tensile strength of the wires in bridge F, and if themesh of the wire-cloth be rectangular in form (as I prefer and haveshown in the drawings) those wires which resist strain will be anchoredby reason of the wires which run across them being unable to movethrough the set concrete, the holding power of each crosswire or anchorbeing equal to the compressive strength of the hardened concrete inwhich it is embedded.

. Still further,to strengthen the conduit there may be placed in thefoundation and in each successive floor wire cloth laid fiat. Thelengths may be joined by overlapping, as concrete will bond the joint;but it will be possible to weave the. cloth in continuous lengths, whichshall reach from manhole to manhole without joints. Even if the archesare not wired the floor-wires alone will insure a proportionally strongstructure.

The conduit structures herein described will resist strains from anydirection. I11 any way that the conduit be distorted by strain the greattensile strength of iron wires will be brought into tension in one halfof its body and the equally great compressive strength of cementconcrete be brought into compression in the other half. I I

For the material inthe body of the conduit I prefer a concrete ofhydraulic cement and sand; but other materials can be usedbituminousconcrete, for instance. I do not limit myself in this particular.

It is not essential that the sides should be perpendicular, nor is itessential that the floor should be fiat, and both may be varied asdesired.

In Fig. 1 I have shown the foundations of the two lower tiers ofsections as provided with open binders or sheets G G of wire-cloth orsimilar material to impart tensile strength to the concrete. Thesebinders may be placed in some or all of the foundations orbodies ofsurrounding material, as desired.

Any of the departures just mentioned, or similar ones, which, however,embody the principles of my conduit, are, I claim,equivalents and withinthe scope of this patent.

Again, in considering the novel feature of a conduit-duct having asmooth continuous floor, upon which are laid inverted channels insections, which are then rigidly and permanently joined, I do not limitmyself to the particular duct shape herein described. The invertedsectional channel on a continuous fioor is a proportionally desirabledevice, whether the shape of the sections be arched, rectangular, orsemicircular, or whether the inverted channel-sections be made single tocomplete a single duct. 7

I claim- 1. As a conduit for electrical conductors a plurality ofinverted channels made in separate and single sections, said sectionsresting upon a flat foundation-floor, which, with the inverted channels,form duct-openings; and the said channels supporting other floors eachone sustaining its complement of inverted channels whereby the conduitcan be made of any width or height and contain any'number of ducts.

2. A conduit for drawing in and drawing out electrical conductorsconsisting of an inve'rted channel made in sections laid end to end andresting upon a flat floor which forms the lower side of said duct, thesaid fioor being composed of a material plastic when first made butsetting to hardness, plastic setting material being also used to formsupporting sides and a covering-top whereby the floor, sides and topbecome an integral support for the sectional channel which serves tohold it rigidly in position.

3. A conduit for electrical conductors consisting of a foundationhavinga floor formed on the surface thereof, and an inverted channelsection superimposed upon said floor which completes the duct, saidchannel being composed of material plastic when first made but whichsets to hardness and an open frame or binder incorporated into thematerial of said inverted section and conforming to the shape of theinner wall thereof, substantially as described.

4. A conduit for electrical conductors consistin g of a smooth fiatfloor of indefinite width upon which are placed side by side a pluralityof ducts, each duct being formed by superimposing upon said fioorinverted channels in sections placed end to end, the said sections ofeach duct being rigidly and permanently joined at their ends as well aswith the sections of other ducts at their sides whereby the wholestructure is bonded together.

5. As a conduit for electrical conductors the section G laid end to endupon a fiat floor and joined at ends by bridges F the sections G,bridges F and floor being all joined by a setting cement whereby themetallic frameworks 9 are anchored and caused to contribute tensilestrength to the structure as a whole.

6. A conduit-duct for electrical conductors consisting of a smooth flatfioor of indefinite length, said fioor being a composite made byembedding a metallic frame in cement, concrete or other like plasticmaterial whereby the concrete acts as a resistance to compressive strainand the iron wires as resistance to tensile strain; and upon which aresuperimposed in sections inverted channels placed end to end.

7. In an underground conduit, the combination with a foundation ofconcrete, or similar material, having a floor formed on the surfacethereof, of an inverted channel resting upon said fioor whereby thefioor forms the bottom of the conduit, and a body of concrete, orsimilar material, inclosing and surrounding said inverted channel andformed integral with the concrete constituting the foundation,substantially as described.

8. In an underground conduit, the combination with a foundation ofconcrete, or similar material, having a floor formed on the surfacethereof, of an inverted channel placed 'upon said floor so that thefloor forms the body of concrete, or similar material, inclosing andsurrounding said second inverted channel and formed integral with saidsecond body of concrete, substantially as described.

CHARLES HENRY SEWALL.

Witnesses:

FREDERIO A. DEACON, ALFRED J. GREATHEAD.

